Neaten up the handling of configure script regeneration in client.mk.

Add a new 'configure-files' target, just for updating
autoconf-generated files.

client.mk

@@ -162,6 +162,7 @@ endif
 
 endif # MOZ_BUILD_PROJECTS
 
+# 'configure' scripts generated by autoconf.
 CONFIGURES := $(TOPSRCDIR)/configure
 CONFIGURES += $(TOPSRCDIR)/nsprpub/configure
 
@@ -274,20 +275,15 @@ EXTRA_CONFIG_DEPS := \
 	$(wildcard $(TOPSRCDIR)/build/autoconf/*.m4) \
 	$(NULL)
 
-$(TOPSRCDIR)/configure: $(TOPSRCDIR)/configure.in $(EXTRA_CONFIG_DEPS)
+$(CONFIGURES): %: %.in $(EXTRA_CONFIG_DEPS)
 	@echo Generating $@ using autoconf
-	cd $(TOPSRCDIR); $(AUTOCONF)
-
-$(TOPSRCDIR)/nsprpub/configure: $(TOPSRCDIR)/nsprpub/configure.in $(EXTRA_CONFIG_DEPS)
-	@echo Generating $@ using autoconf
-	cd $(TOPSRCDIR)/nsprpub; $(AUTOCONF)
+	cd $(@D); $(AUTOCONF)
 endif
 
 CONFIG_STATUS_DEPS := \
-	$(TOPSRCDIR)/configure \
+	$(wildcard $(CONFIGURES)) \
 	$(TOPSRCDIR)/allmakefiles.sh \
 	$(TOPSRCDIR)/.mozconfig.mk \
-	$(wildcard $(TOPSRCDIR)/nsprpub/configure) \
 	$(wildcard $(TOPSRCDIR)/directory/c-sdk/configure) \
 	$(wildcard $(TOPSRCDIR)/config/milestone.txt) \
 	$(wildcard $(TOPSRCDIR)/config/chrome-versions.sh) \
@@ -307,7 +303,9 @@ ifdef MOZ_TOOLS
   CONFIGURE = $(TOPSRCDIR)/configure
 endif
 
-configure:: $(CONFIGURES)
+configure-files: $(CONFIGURES)
+
+configure:: configure-files
 ifdef MOZ_BUILD_PROJECTS
 	@if test ! -d $(MOZ_OBJDIR); then $(MKDIR) $(MOZ_OBJDIR); else true; fi
 endif